1. Field of the Invention
This invention relates to an off-the-highway vehicle tire and more particularly a tread design adapted to provide improved performance characteristics of the vehicle tire. Specifically, the instant invention relates to an alternating lug tread design employing long and short lugs alternately disposed about the periphery of the tire in a substantially symmetric manner whereby lugs from each side of the tire strike the ground substantially simultaneously thereby minimizing the side forces which occur when lugs on either side of the tire are offset.
2. Description of the Prior Art
The use of an alternating lug tread design for tires adapted for off-the-highway vehicles is well known in the art as shown by U.S. Pat. No. Des. 104,492 to Brunner, U.S. Pat. No. Des. 169,668 to Hardeman, U.S. Pat. No. Des. 213,659 to Petroff, U.S. Pat. No. 3,844,326 to Verdier which discloses a tread design having two adjacent, oppositely oriented rows of L-shaped relief elements arranged so as to form wide lateral recesses between their adjacent long arms forming the lateral portions of the tread and narrow central grooves between their adjacent arms forming the central portion of the tread, U.S. Pat. No. 4,131,148 to Bertazzoli, et al, which discloses an agricultural tire tread with symmetrical lugs along each side of the tread and spaced in a repeating and angular pattern from the sidewall of the tire to the centerline, U.S. Pat. No. 4,186,788 to Pommier, which discloses a tractor tire tread having a repeating pattern of opposing and alternating lugs of the same size on each side of the tire whereby each lug extends from the side of the tire and overlaps the centerline of the tire, and Canadian Pat. No. 648,244 to Davis, which discloses an agricultural or earthmover tire tread design embodying a repeating and alternating pattern of lugs wherein the long lug extends from one side of the tire to the other and the short lugs extend to a point just beyond the centerline of the tire tread.
The use of an alternating short and long lug tread design for an off-the-highway vehicle is also well known in the art as disclosed by U.S. Pat. No. 3,603,370 to Hylbert et al, which discloses a rear tractor tire having a tread with alternating long and short lugs on each side, each long lug having an inner portion extending at a low angle with respect to the mid circumferential centerline of the tread and an outer portion extending at a high angle with respect to said mid-circumferential centerline, and each short lug being disposed at a high angle with respect to said mid-circumferential centerline, and Australian Pat. No. 156,404, which discloses an improved method of relugging tires which shows an off-the-road vehicle tire having a series of alternating short and long lugs.
Although the above-noted prior art discloses several designs for off-the-highway type tires, including designs incorporating alternating long and short lugs, the tire designs of the prior art generally cause poor ride characteristics of the tires due to their asymmetrical design which causes adjacent portions of their tread to unevenly contact the ground causing uneven side forces on the tread thus producing a poor ride characteristic of the tire. Specifially, it should be noted that the tread designs of the prior art disclose designs having a generally asymmetrical design which has contact portions of the tread which cause uneven contact of the tread with respect to its supporting surface. The uneven contact of the tread with respect to its supporting surface results in a side force on that portion of the tread that does contact the supporting surface. The side force has a tendency to induce vibration in the tire and generally produce a poor ride characteristic.
There is, therefore, a need for an off-the-highway vehicle tire which provides improved ride characterstics by providing a substantially symmetric tread pattern.